1. Technical Field
This disclosure relates to an image forming apparatus, and more specifically to an image forming apparatus, such as an inkjet recording apparatus, copier, printer, facsimile machine, plotter, or printing device, having a clutch assembly to perform drive switching to switch back a sheet at a position downstream from an image forming device.
2. Description of the Related Art
For image forming apparatuses capable of performing duplex printing (printing images on both front and back faces of a sheet of recording media), the drive switching for switching back the sheet is performed by (1) an additional actuator, such as a clutch, or (2) a pivoting gear. In an example of the drive switching performed by (1) a clutch or additional actuator, a duplex-printing transport switching section (switchback mechanism) to transport a sheet to a duplex-printing transport path after image formation is disposed downstream from an image forming section (including a fixing device). After image formation on a first face of a sheet, the sheet is switched back by a sheet output section and transported into the duplex printing transport path (see, for example, JP-2008-285279 and JP-2007-076881).
In JP-2008-285279 and JP-2007-076881, a clutch having a solenoid serving as additional actuator (a combination of a pivoting gear and a link mechanism or a combination of a pivoting gear and a switching guide) and its driving connection method are proposed to obviate driving sources rotatable in forward and reverse directions and perform the switchback operation by a single driving source.
In an example of the drive switching performed by (2) a pivoting gear, in an image forming apparatus that conveys a sheet by a conveyance belt and forms an image on the sheet on the conveyance belt, a duplex transport path switching section to transport a sheet to a duplex transport path (duplex transport route) after image formation is disposed upstream from an image forming section. After the end of printing (image formation) on a first face of the sheet, the sheet is switched hack by the driving of the conveyance belt in reverse direction and is transported into the duplex transport path.
For such a configuration, the sheet is always reversed in the duplex transport path, and the surface of the conveyance belt is rotated in both forward and reverse directions to convey the sheet. Hence, as an art to drive with a single driving source, for example, JP-2005-148365-A proposes to connect driving of the duplex transport path via a pivoting gear without a clutch.
However, for conventional arts, including the arts described in JP-2008-285279 and JP-2007-076881, in which the drive switching for switching back the sheet is performed by an additional actuator, such as a clutch, the size and cost of the image forming apparatus may increase.
For a driving connection method using a pivoting gear (including the art described in JP-2005-148365-A), a duplex transport path switching section to transport a sheet to a duplex transport path after image formation is disposed downstream from an image forming section. A duplex transport path is formed to switch back the sheet at a sheet output section after an image is formed on a first face of the sheet and guide the sheet having the image on the first face to a non-opposing face of a conveyance belt not opposing an image forming device or a non-opposing side of a conveyance roller not opposing the image forming device. In such a case, if a pivoting gear is used, the pivoting gear is disposed in a driving system connected to the conveyance roller, thus hampering high-speed control of the conveyance belt or high-precision and high-speed control of the transport amount of the sheet conveyed by the conveyance belt (e.g., a transport amount control to determine the position of the sheet in unit of micrometer in several tens of milliseconds).
In addition, typically, a direct current (DC) motor is used as the driving source. If the pivoting gear is intermediately disposed in the driving system from the DC motor to the conveyance roller to drive the conveyance belt via a driving force transmission device, e.g., a timing belt, the intermediation of the pivoting gear reduces the driving stiffness of the driving system. Alternatively, when a high frequency is input to drive the DC motor, the DC motor may oscillate or increase the time constant. Consequently, since only a low frequency can be input to the DC motor, the activation of the DC motor may slow, thus hampering high-speed control of the conveyance belt or high-precision and high-speed control of the sheet transport amount.